Headers, Gears, and a Posi Are Worth Almost a Full Second

Step By Step

Headers and a larger cat were the first changes for the Camaro this month. We chose Edelbrocks emissions-legal headers that include the smaller 2-1/4-inch lead-down pipe to the catalytic converter. Edelbrock also makes a larger system for the H.O. engines using a 3-inch lead-down pipe. To make this system breathe, we also installed a 3-inch DynoMax catalytic converter.

Tim removed the Edelbrock 2-1/4-inch lead-down pipe and replaced it with a section of 3-inch tube. This looks like a big jump, and it is since the 3-inch tubing is over 80 percent larger than the smaller tubing. This should help the Camaro when we add the heads and cam.

Next up on our test agenda was a set of 3.73 gears and a Posi. Tim liberated all these parts out of the local boneyard for less than $50. Tim also installed the gears himself, but you can expect to pay around $100 to $200 to have this done.

Ratech supplied this deluxe installation kit that includes both pinion and carrier bearings, pinion seal, crush sleeve, and pinion nut. We also included a Ratech solid-shim spacer to replace the crush sleeve, which improves the 7.5-inch ring gear 10-bolts durability.

At the track we discovered a sticking secondary air-valve door on the Q-jet that delayed the opening of the secondaries. With a little minor surgery, we repaired the problem. The nearby screw (arrow 1) deforms the soft metal and catches the air-valve door. You can also see the secondary metering rod hanger in this photo (arrow 2) retained by a Torx head screw.

The metering rod power tip diameter determines the amount of fuel metered. Larger tips allow less fuel while smaller tips meter more fuel. All Q-jet metering rods are stamped with a two-letter designation that determines their size. We used an AU rod that seemed to work best.

Secondary hangers are critical to achieving the proper air/fuel ratio with a Q-jet. A single letter identifies hangers. The difference between each hanger is 0.005-inch in height. As you can see, the D hanger on the left will pull the metering rods out of the fixed jets much farther than the O hanger on the right. The difference is 11 steps, or 0.055 inch.

The Camaro still doesnt leave very hard, with only a 2.38-second 60-foot time, but we managed to improve the e.t. another 0.47 second. Overall, the Camaro has now run an altitude-corrected quickest time of 15.82 at 86.74 mph. CHP

Third-generation Camaros make wonderful budget builders, because you can buy them dirt-cheap. If you've just joined our performance buildup, this is the third part of a multi-part performance construction project where we started with a basic carbureted LG-4 305ci small-block with a TH700-R4 and a lazy 2.73 rear gear. The best part is that our pal Tim Moore bought this jewel for a paltry $271. Up to this point, we've added an intake manifold, a dual-snorkel air cleaner, a stronger mechanical fuel pump, and an after-cat exhaust. The Camaro responded with minor e.t. and speed improvements, but what it really needed was headers and a gear.

It's tough to make power if the air and fuel gets in but can't get out. Last month, we added an intake manifold and air cleaner, enhanced with a larger after-cat Flowmaster exhaust system. Unfortunately, our little 305ci engine was still trying to exhale through stock iron exhaust manifolds, a 2--inch Y-pipe, and the stock replacement catalytic converter. The first order of business was a set of headers. We searched through several header kits and settled on Edelbrock's 1-5/8-inch headers for the early third-gen Camaros.

The headers are completely smog-legal since they retain the original air injection reaction (A.I.R.) fittings to inject fresh air into the exhaust to help reduce hydrocarbon (HC) emissions. Car-owner Tim Moore reported that he had to move the steering column to fit the driver-side header in place. The passenger-side pipes also required some finesse to install.

The final part of the job involved some modification to the Y-pipe. We ordered the headers for a standard 305 Camaro, not the High Output (H.O.). The H.O. systems use a larger 3-inch catalytic converter, which dictates using a 3-inch Y-pipe from the headers to the catalytic converter. Since we ordered the smaller header system before we realized that we needed a 3-inch catalytic converter, Tim decided to modify the existing Y-pipe to increase it to the 3-inch size. The easier thing to do would probably be to order the H.O. headers and exhaust, and the whole system would bolt together.

We also needed a larger catalytic converter to help this engine breathe. These early systems used a single catalytic converter, so a larger 3-inch converter is essential for better breathing. DynoMax offers several universal high-performance catalytic converters, and we selected the 3-inch inlet and outlet converter. Once the converter was in place, the entire header and new converter conversion operation required the better part of eight hours to complete. Since Tim was able to do the work himself, we didn't have to pay for labor, but you could expect to pay over $400 for a muffler shop to perform this task.

Before we moved on to the gears and Posi, we decided to test the Camaro at Los Angeles County Raceway (LACR) to evaluate the performance improvement. We were expecting around a half-second improvement and hoped we might see more. LACR offers a Wednesday night test night, so we bopped up to the high desert. Even though this was an evening excursion, the air was still plenty thin with a density altitude of 4,400 feet (see "Altitude Adjustment" for more information on density altitude). At first, the Camaro was hesitant to deliver, but with a cooler engine and a higher shift rpm of 6,300 rpm, the Camaro responded with a corrected 16.29/86.59-mph pass that was a 0.46-second and 2.3-mph improvement over the previous test.

These were encouraging improvements, even if we still were only running low 16s. But still, the Camaro was going through the lights in Second gear, and we knew that what we really needed was a deeper rear gear. It was time to get serious.

Roughly a month before, we had been touring our local Pick Your Part self-service recycling yard and ran across a 2.8L V-6-powered Blazer with the standard 7.5-inch, 10-bolt rearend. Tim knew that many of these tiny V-6-powered SUVs came with a deeper 3.73 gear to give them some help from the stoplight. Someone had already relieved the dead Blazer of its spider gears, which made removing the ring-and-pinion a snap. The gears were on an open carrier, so we unbolted the ring gear and managed to walk out with an excellent set of 3.73 gears for a paltry $22.50.

A couple of days later, Tim found a Posi unit in a third-generation Camaro for a mere $25, so for less than $50, we had gears and a Posi-traction unit. We then ordered the deluxe Ratech rebuild kit through Summit for $120, which offered all the bearings and parts we needed to install the new gears. While we could have cheaped out on the bearings, we figured this would give us a virtually brand-new rear axle that could probably take most of the abuse we could dish out. Again, Tim installed the gears himself so we didn't have to add any labor to our running bill. However, you can expect to pay around $100 to $200 to have a professional shop install the gears.

With new lube in the rear axle, it was once more time to hit the track. Tim again drove the Camaro back up to LACR. Now the Camaro was much more responsive and much more fun to drive. Usually, a 3.73 gear is a pain to drive on the freeway because the rest of the world is cruising at 75 mph and you're stuck at 60 or 65 mph. But with the TH700-R4 overdrive, the effective rear-axle ratio in overdrive computes out to 2.83:1, which is extremely comfortable to drive. With our 26-inch tall rear tires, the cruise rpm was a paltry 2,560 rpm at 70 mph.

The best news was what happened at the track. The one full point of additional gear ratio made a big difference. The 305 still doesn't have the torque to fry the tires, but this means it doesn't spin the tires hard enough yet to require an investment in sticky tires. After a little tuning with secondary metering rods (we found an AY secondary metering rod worked the best), the Camaro cranked out a corrected 15.82/86.74 which was a stout 0.47-second improvement over the previous combination. The mph picked up only slightly, but we were also facing a very stiff wind that night that got so bad it knocked our last run down by 7 mph! The Camaro would probably be 1 to 2 mph faster in better conditions than the speeds we've reported here.

Combined with the headers, gears, and Posi, the Camaro is now a full 1.6 seconds quicker and 8 mph faster than it was a mere two months ago. Not only that, but the Camaro also has a street presence now with its more authoritative exhaust note, and enough gear to take maximum advantage of the remaining modifications. In an upcoming story, we're going to bolt on an emissions-legal Crane hydraulic roller cam and a set of World Products S/R Torquer heads that should put some power to the ground. Our goal is to run in the high 14s. That's a lofty goal considering that we'll need to pick up over 0.80 second just to run a 14.99. We're not sure the 170,000-mile short-block and rings can seal the cylinder pressure needed to do that, but it should be interesting to find out.

Our '87 Camaro is shaping up nicely as a real-world performance car. It's already fun to drive, still gets over 20 mpg on the freeway, and is slowly becoming quicker every day. We can't wait until next time.

Sources

Headers and a larger cat were the first changes for the Camaro this month. We chose Edelbrocks emissions-legal headers that include the smaller 2-1/4-inch lead-down pipe to the catalytic converter. Edelbrock also makes a larger system for the H.O. engines using a 3-inch lead-down pipe. To make this system breathe, we also installed a 3-inch DynoMax catalytic converter.

Tim removed the Edelbrock 2-1/4-inch lead-down pipe and replaced it with a section of 3-inch tube. This looks like a big jump, and it is since the 3-inch tubing is over 80 percent larger than the smaller tubing. This should help the Camaro when we add the heads and cam.

Heres a worms-eye view of the exhaust with the larger DynoMax cat and the 3-inch Y-pipe in place. Adding the headers and cat were worth a 0.46-second and 2.3-mph improvement.

Next up on our test agenda was a set of 3.73 gears and a Posi. Tim liberated all these parts out of the local boneyard for less than $50. Tim also installed the gears himself, but you can expect to pay around $100 to $200 to have this done.

Ratech supplied this deluxe installation kit that includes both pinion and carrier bearings, pinion seal, crush sleeve, and pinion nut. We also included a Ratech solid-shim spacer to replace the crush sleeve, which improves the 7.5-inch ring gear 10-bolts durability.

At the track we discovered a sticking secondary air-valve door on the Q-jet that delayed the opening of the secondaries. With a little minor surgery, we repaired the problem. The nearby screw (arrow 1) deforms the soft metal and catches the air-valve door. You can also see the secondary metering rod hanger in this photo (arrow 2) retained by a Torx head screw.

Q-jet secondary metering is controlled by metering rods that fit into fixed jets in the carburetor body.

The metering rod power tip diameter determines the amount of fuel metered. Larger tips allow less fuel while smaller tips meter more fuel. All Q-jet metering rods are stamped with a two-letter designation that determines their size. We used an AU rod that seemed to work best.

We learned this tip from Curt Hooker at Edelbrock. He uses a length of cardboard to organize his Q-jet metering rods in order by power tip size.

Secondary hangers are critical to achieving the proper air/fuel ratio with a Q-jet. A single letter identifies hangers. The difference between each hanger is 0.005-inch in height. As you can see, the D hanger on the left will pull the metering rods out of the fixed jets much farther than the O hanger on the right. The difference is 11 steps, or 0.055 inch.

The Camaro still doesnt leave very hard, with only a 2.38-second 60-foot time, but we managed to improve the e.t. another 0.47 second. Overall, the Camaro has now run an altitude-corrected quickest time of 15.82 at 86.74 mph. CHP

Follow along as our 1983 Chevrolet Camaro has its suspension worked over with an assortment of handling upgrades for third-gen Chevy Camaros and then we put it to the teat on the track - Super Chevy Magazine » Read More